Orogen holds 1% NSR royalty
Owned by AngloGold Ashanti
Precious metal deposits in the Southwest Nevada Volcanic Field (SWNVF) have combined production and reserves of greater than 60 t of Au and 150 t of silver (Castor and Weiss, 1992). Silicon is located in the Bare Mountain district where gold was discovered in 1905. The first underground workings were developed at the Panama mine on a breccia zone that averaged 0.4 oz/st Au (Gillstrom, 2006). Modern mining began with an open pit at Sterling in 1980 which produced 194,000 ounces of gold at an average grade of 0.217 oz/st between 1980 and 2000 (Gillstrom, 2006). Imperial Metals reopened the Sterling Mine in 2012 as an underground mine and identified additional underground gold resources at the 144 zone (Gillstrom, 2006). Northern Empire Resources acquired the property form Imperial in 2016 and was subsequently acquired by Coeur Mining in 2018
Orogen’s Silicon property includes multiple small historic pits and underground mines. The workings exploited mercury and porcelain-grade silica from cinnabar bearing steam heated and acid leached alteration zones.
The Silicon property is located in the Southwest Nevada Volcanic Field (SWNVF) on the western margin of the Timber Mountain caldera. The stratigraphy is dominated by Miocene rhyolitic tuffs. Intense acid leaching has affected many of the rocks in the property, variably altering them to alunite, kaolinite, chalcedony, opal and residual silica. Based on gravity data and regional geology, the property overlies a basement high on the southwestern margin of the Timber Mountain Caldara.
Mineralization occurs as cinnabar-bearing chalcedony, opal and acid-leached residual silica in rhyolitic host rocks. Elsewhere in the Bare Mountain district, mineral deposits include disseminated sediment-hosted "Carlin-Like" gold mineralization at the Sterling deposit, volcanic-hosted, low-sulfidation gold mineralization associated with a quartz-adularia-calcite mineral assemblage at the Secret Pass deposit, and gold in breccia pipes associated with quartz, opal, alunite, and pyrite at the Telluride mine (Castor and Weiss, 1992). The deposits appear closely related in age and may represent different levels of exposure in several hydrothermal systems that may include one or more buried porphyry systems. The shallowest expressions of the systems are the mercury-bearing acid-leached volcanic rocks exposed on the Silicon property.
Orogen used detailed structural geology and lithologic and alteration mapping merged with geophysics to target concealed precious-metal zones at Silicon. Regional gravity data imply the existence of a Paleozoic bedrock ridge projecting north from the Telluride and Secret Canyon mines into the Silicon property. Multiple centers of shallow-level advanced argillic alteration spatially overlap the bedrock ridge. Within these alteration zones, the mercury-mineralized surface structures are high priority targets because of their potential to transition into precious-metal- bearing veins at depth. A grab sample from an old drill cuttings pile contained 114 ppb Au, which supports the hypothesis that gold concentrations increase with depth. The likely intersection of hydrothermally altered structures with the Fluorspar Canyon detachment fault at the top of the underlying carbonate sequence is also a strong target for precious metal mineralization, because of the potential for structurally controlled hydrothermal fluids to interact with favorable silty, sandy beds in the underlying carbonate sequence to form "Carlin-like" deposits. In any case, the high grade gold mined elsewhere in the district indicates the systems exposed at the Silicon property have the potential to produce profitable underground-mineable deposits.